Large-scale presses, especially bulky part multiple-die presses, are provided with rams, which are moved vertically up and down by a main drive for the press. Eccentric drives are used, for example, for lifting and lowering the rams. To even out the movement and remove a load from the drive, pneumatic cylinders containing vertically displaceable pistons are frequently installed above the ram, wherein a piston rod that is subjected to a pull is connected to the ram. The pneumatic cylinders generate a pull in an upward direction, which partially or totally compensates or counter balances the force of the ram weight.
To compensate for the considerable weight of a ram, the pneumatic cylinders must have a considerable size. They consequently hold a corresponding compressed air volume that can exceed one cubic meter. Since the energy stored therein is considerable, care must be taken to ensure that this energy does not become dangerous. For example, if the piston rod of the pneumatic cylinder breaks off as a result of material fatigue or another type of material defect, the force of the gas bolster or cushion enclosed inside the pneumatic cylinder acts upon the piston and accelerates it. Given an unfavorable arrangement, the piston can then shoot out of the pneumatic cylinder in the manner of a projectile.
Starting with this premise, it is the object of the present invention to provide a pneumatic force-generating device for keeping the resulting danger in check, even during the sudden removal of a counter force for the connected device.